Disclaimer: I am not J K Rowling. I do not own Harry Potter.
Note: The following takes place in an alternate universe, after the Gryffindor/Slytherin quidditch match in Harry's first term, where Quirrell/Voldemort has implemented different plans from canon to get hold of the philosopher's stone.
Further Note: This is a one-shot, which occured to me when I should have been writing something else.
Further Note: Updated/tweaked slightly in last few lines.
With a gesture that most observers would have found to have had an unexpected tenderness, coming from the Hogwarts' potions master, Severus Snape reached over and closed Harry Potter's eyes, which were staring sightlessly at the infirmary ceiling.
"He's gone, headmaster. I don't know what kind of upbringing those muggles you sent him to live with gave him, but he was too weak to pull through."
The infirmary was full to overflowing. All the other members of the Gryffindor quidditch team were there, as were many of their close friends and supporters.
The eyes of Albus Dumbledore were grave.
"The stone's gone, Severus. This was the perfect diversion." the headmaster said.
"The stone?" Severus said softly and very dangerously. "Is that all you care about, headmaster? Your defence against the dark arts teacher, Professor Quirrell, whom I told you was up to no good – to which you responded that you had 'everything under control' – has poisoned in excess of three dozen Gryffindor students, some of whom are fighting for their lives, and many of whom, even if they pull through, may suffer unpleasant effects for the rest of their lives. Harry James Potter, whom you were supposed to have plans for, is dead. And all you can think about is a worthless piece of rock which shouldn't have been in a school full of students in the first place?"
The Gryffindor against Slytherin quidditch match had passed without a hitch for Gryffindor – although some of the Slytherin students seemed to have had trouble at crucial moments with controlling their brooms. And then a very large chocolate-cake covered with green icing and a small quidditch pitch model in marzipan had turned up in Gryffindor Tower, with a note 'congratulations to the Gryffindor team and their friends'. The note had even been signed Professor Quirrell. And of course, the Gryffindors had had no reason to not trust a cake sent by a Hogwarts professor…
"It was your old master, Voldemort." Albus Dumblore said. "He's been hiding under Quirinus' turban, and now Quirinus has the stone Voldemort will be able to gain a new body."
"You knew Voldemort was possessing Quirrell and you still let him into the school this year?" Severus stared in disbelief. "You let a dark lord into a school full of children? What were you hoping to achieve, headmaster? To give him a couple of lemon drops and convince him to repent of his evil ways?"
"I thought it would prove an appropriate test, for Harry. In a controlled environment."
"Oh Merlin, you didn't really want us to protect the stone did you, you wanted some sort of gauntlet for a first year to run through? Well, I hope you're happy now." Severus gestured to the boy lying unmoving in the bed. "Voldemort passed your test with flying colours. Now, if you'll excuse me, but I have students who are still alive and breathing whom your 'wisdom' hasn't yet managed to kill, whom I would like to help Madam Pomfrey to stay that way."
Severus Snape spun on his heel and walked away from the headmaster.
"You sent for me, sir?" Neville Longbottom arrived in Professor Snape's office, shortly after dawn had broken. A Hogwarts elf had delivered the professor's summons to Neville.
"There has been a family emergency at your home, Mr. Longbottom." Professor Snape said. Professor Snape looked tired, Neville thought. It was said that he'd been up all night in the infirmary, trying to treat victims. Neville Longbottom hadn't been anywhere near the poisoned cake, because he'd been locked out of Gryffindor Tower immediately after the match, having forgotten the portrait password yet again. "Professor McGonagall has requested I escort you from the premises and apparate you back to your grandmother."
Neville nodded, dumbly.
Albus Dumbledore sat in his office. His pensieve was currently filled with the silvery memory of a certain prophecy that had once been delivered to him. He'd slept on his predicament, to help clear his mind, and upon awakening he'd reviewed his memory of the prophecy straight away.
He hadn't been expecting things to go wrong like this. He had had his usual clever plans, and his clever plans always worked out just fine. Except this time, of course they hadn't.
He felt numb, and couldn't understand why Quirrell/Voldemort had poisoned all those children with something so dangerous? I mean, yes, it had made a fine diversion for a grab for the stone, but the man should have had some kind of restraint. Hadn't he loved Hogwarts when he was a child? Weren't some of the victims of his poisoning the sons and daughters of the pure-blood families he had once espoused to be protecting? True, they had been Gryffindors, and that almost certainly would have made them from families which were likely blood-traitors to Voldemort's mind, but to try and kill so many all in one go?
Albus just didn't understand how Tom could have come to be in this state.
There was one silver lining though, in all of this, which Albus was going to have to grimly cling to, through the storm of enquiries which was to come, in which he was going to have to lie through his teeth and explain that of course he had no idea that Quirrell could have been any real threat to the pupils, and that Nicolas Flamel had been so essential to British wizarding society that Albus had had no choice but to keep the stone here. That silver lining was that arguably Harry Potter had just died 'at the hand of the other' in the sense of being poisoned by Voldemort (especially if Quirrell/Voldemort had personally made the cake, which Albus strongly suspected given the poison was strengthened by attempted bezoar treatment, as one of the Weasley twins had been almost killed finding out) so the prophecy was now done and dusted, and other people could handle Voldemort just fine. That was but a very small crumb of comfort though, in the face of this loss.
At least Albus still had the Longbottom boy in reserve, if the prophecy should somehow still be in play…
Note that poisoning people in Hogwarts is demonstrably effective in canon, in that Draco Malfoy almost manages to kill someone in book 6 without his poison being detected before it is consumed. Only the presence immediately to hand of emergency treatment saves that person's life.
Whatever it is that Quirrell/Voldemort used in this story, it isn't quite so concentrated and fast acting as what Draco employed in book 6 in canon (Quirrell/Voldemort wants the most people possible to consume it, before victims start to show symptoms, to maximise potential casualties and his diversion), but it is tailored to resist some of the most obvious forms of treatment.
And, well... Harry was probably being fed cake as the star player and because he didn't things like that that often at Privet Drive... okay, Quirrell/Voldemort was fortunate that Harry was a fatality, but it seems to me credible that all things being considered he would be a credible casualty, despite the fact that he would no doubt have been specifically picked out by the headmaster with orders 'save this pupil if you possibly can'.
This was written partly as a reaction to canon Dumbledore always having convoluted plans which still somehow manage to play out wth minimum serious disruption from the villains. (I believe on another website, he's described as playing 'Xanatos Roulette'.) This time when Dumbledore bets the farm on the ball coming up 'lucky seven', for once it comes up something else instead.
As a reminder, this story is a one-shot.